Book 1980's - Bikers, Time Travel, Volcano - Help?

I've been looking for this book for years, i bought it at a place called Rainy Day Books, it has since closed down. On the front cover, it had a Volcano in the back-ground, flying saucer in the air, Bikers "in the book the bikers were described as being Allot tougher than hell's angels bikers? The story starts with a man, waking up in this strange place "i think? i don't remember much about the protagonist as the story was more about the strange people and things that happened to him than about him." All i remember is the book read Allot like Spider Robinson's Crosstime Salloon only outdoors? It had bikers, aliens, time travel, and a race to save the people in the city from some disaster. I know that's all a vague description but its all i remember from that long ago, i can't remember the author or the book title, only that the front cover was very colorful. hope somone has read this besides me.